Solid flow characteristics of mixed-sized oil shale in vertical pneumatic conveyers were investigated using a 47.6-mm-diameter lift-pipe. The shale was in a crushed and spent condition with a particle size range of 0.074 to 3.36 mm. Components of the pressure gradient in established flow were measured over a range of gas velocities and solid fluxes. Size-dependent particle velocities were also indirectly measured and shown to depend on solid flow rates. Particle velocity dependence is described by experimentally generated expressions for the range of particle sizes studied. In this system for conveying mixed-sized shale, particle velocities were found not to be predictable from terminal or free-fall velocities which were also measured. The aggregate solids velocity, which is computed from the single-sized particle-velocity relations, permits a reasonably accurate prediction of solids pressure drop. Use of a solids friction factor, estimation of choking velocity, and characteristics of the acceleration length are also discussed. 18 figures, 4 tables.